In multi-carrier systems with carrier aggregation, a user terminal may be paired to or monitor adjacent multiple carriers associated with the same or multiple base stations. The user terminal may also be paired to or monitor multiple carriers associated with the same or different base stations in different frequency bands. Additionally, asymmetric carrier aggregation is possible in frequency division duplex (FDD) mode with different numbers of downlink and uplink carriers aggregated for a user terminal; under these circumstances, one or more of the downlink/uplink carriers do not have a corresponding or associated uplink/downlink carrier (fixed channel spacing). It may also be possible that only a subset of carriers being aggregated (e.g., carriers served by a base station) have a common scheduler (possibly a common MAC entity) resulting in multiple independent schedulers for different subsets of the aggregated carriers.
In some multi-carrier systems, generally, transmit power control (TPC) can be configured independently for different aggregated uplink carriers or a subset of aggregated uplink carriers. Independent TPC may be used to support different quality of service (QoS) requirements, different traffic types with different block error rate (BLER) operating points and different interference levels (IoT) across different aggregated carriers. In some implementations, multiple PAs serve multiple aggregated carriers, for example, aggregation across different frequency bands with a power amplifier for each band.
Per-component carrier TPC and closed-loop power control (PC) commands also provide an additional degree of freedom to adjust UE power in addition to modulation coding scheme (MCS) adaptation, for example, near the lowest/highest MCS settings. In 3GPP LTE, per-component carrier TPC requires the definition and signaling of carrier-specific open loop power control parameters such as P0, α and PL and possibly closed loop PC command δPUSCH/δPUCCH. In the following description we assume independent power control for the different carriers. However, the details are also applicable for the case when common power control is performed for a group or subset of carriers.
A component carrier specific power control has also been proposed in R1-090738. The LTE Rel-8 power control for a single carrier can be straightforwardly extended to support component carrier specific power control as suggested in R1-090738.
The various aspects, features and advantages of the invention will become more fully apparent to those having ordinary skill in the art upon a careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.